Students in AP C were introduced to the topic of “2-body systems” today with a tutorial from Tutorials in Introductory Physics. In the tutorial, students draw forces diagrams for each object in a two-body system and are lead through a series of questions to help them identify and realize how Newton’s 3rd Law can help them identify and compare forces in this force diagram, and how other rules (Newton’s 2nd and how friction works) can be used to help them rank the forces involved. Almost everyone “misses” one of the 3rd law pair forces acting between the two objects and incorrectly identifies equal and opposite forces as Newton’s 3rd Law force pairs, until prompted by questions in the Tutorial. This set us up to be able to determine the value of these internal forces and the acceleration of a system in situations where two objects are interacting and accelerating together.
Randall Physics 